1. Field of Invention
The present invention relates to giant magnetoresistance (xe2x80x9cGMRxe2x80x9d) transducers or read heads for reading magnetic signals from magnetic recording media, and more particularly, to current perpendicular-to-the-plane giant magnetoresistance (xe2x80x9cCPP-GMRxe2x80x9d) designs. While the invention finds particular application in conjunction with reading hard disk drives, the invention can be implemented with other magnetic storage media. Moreover, the invention can be implemented in other magnetic field detection devices as well as in other devices and environments.
2. Description of the Related Art
Giant magnetoresistance (GMR) was initially described by Baibich et al. in Physical Review Letters, Volume 61, No. 21, pp. 2472-2475 (1988) which is hereby incorporated by reference. GMR occurs when an application of an external field causes a variation in the relative orientation of the magnetizations of neighboring ferromagnetic layers. This in turn causes a change in the spin-dependent scattering of conduction electrons, thereby changing the electrical resistance of the structure. The discovery of GMR triggered a wide study of transport properties of magnetic multilayers. In most cases, the current flows in the plane of the layers, called CIP-MR.
Pratt et al. extended the GMR measurements to the case where the current flows perpendicular-to-the-plane, called CPP-MR, as described by Pratt et al. in Physical Review Letters, Volume 66, pp. 3060 (1991), which is hereby incorporated by reference. In general, the CPP-MR effect is several times larger than the CIP-MR effect. For magnetoresistance (MR) read head applications, the CPP-MR element has to be dramatically scaled down ( less than 100 nm) because of the very small specific resistance of the MR element with the CPP configuration.
U.S. Pat. No. 5,627,704 and U.S. Pat. No. 5,668,688 (which are both hereby incorporated by reference) have described the application of CPP-MR for magnetic transducers. In both cases, a longitudinal magnetic bias means was provided as usual by permanent magnets located at the sides of the GMR structures. With longitudinal magnetic bias, the GMR structure must be a spin valve type structure in order to have good linear response in the field of small signals.
In both CIP-MR and CPP-MR, the application of an external field causes a variation in the relative orientation of the magnetizations of neighboring ferromagnetic layers. As discussed above, this in turn causes a change in the spin-dependent scattering of conduction electrons and thus the electrical resistance of the structure. In order to apply CPP-MR for MR heads, a transverse magnetic bias to the CPP multilayer is required in order to achieve an optimum response.
The spin valve structure, as described by Dieny et al. in Physical Review B, Volume 43, pp. 1297 (1991), which is hereby incorporated by reference, discusses a conventional approach of using a GMR structure arranged in a CIP-MR mode within a hard disk drive arrangement. A standard spin valve comprises two ferromagnetic layers separated by a nonmagnetic spacer, such as a layer of Cu. The magnetization of one ferromagnetic layer is fixed by an adjacent antiferromagnetic layer or permanent magnetic layer, and is prevented from rotation in the presence of the field of interest. The magnetization of the other ferromagnetic layer is not fixed, and is thus free to rotate in the presence of an external field.
Essentially, the MR response varies as the cosine of the angle between the magnetizations in the two layers, resulting in a high linear density resolution. However, the SV type CIP-MR heads may nevertheless still not be suited for ultra-high areal density applications due to the inherent limitations resulting from the small read gap of such an arrangement.
U.S. Pat. No. 5,668,688 describes an application of current-perpendicular-to-the-plane (CPP) spin valve type MR transducers or heads, having shields that are also used as leads, resulting in a smaller read gap. Nevertheless, these designs are still not able to achieve an optimum linear response due to the lack of a transverse bias supply arrangement.
A satisfactory linear response can be achieved in a CIP mode SV type MR read head arrangement by utilizing an anti-parallel (AP)-pinned layer, where two ferromagnetic layers are antiferromagnetically coupled through a very thin antiferromagnetic spacer (AFS) such as a layer of Ru, Re, Ir, or Rh. The AFS is typically  less than 1 nm. As shown in FIG. 1, by providing two AP sublayers (AP-pinned 1 and AP-pinned 2) with essentially the same magnetic moment, but arranged in opposite directions, the overall AP-pinned layer has a resultant net moment near zero. This results in a satisfactory SV linear response because of the very small magnetostatic coupling acting on the free layer. However, in a CPP-MR head, such a structure is not appropriate. According to a two current series resistor model described by Lee et al. in the Journal of Magnetism and Magnetic Materials, Vol. 118, pp. 118 (1993), the specific resistance change Axcex94R of this structure can be roughly estimated by:       A    ⁢          xe2x80x83        ⁢    Δ    ⁢          xe2x80x83        ⁢    R    =                                          4            ⁡                          [                                                                    β                    P                                    ⁢                                                            ρ                      P                      *                                        ⁡                                          (                                                                        t                          AP2                                                -                                                  t                          AP1                                                                    )                                                                      +                                                      AR                                          P                      /                      SP                                        *                                    ⁢                                      γ                                          P                      /                      SP                                                                                  ]                                                                        (                                                            β                  F                                ⁢                                  ρ                  F                  *                                ⁢                                  t                  F                                            +                                                AR                                      F                    /                    SP                                    *                                ⁢                                  γ                                      F                    /                    SP                                                                        )                                                                                                  ρ                F                *                            ⁢                              t                F                                      +                                          ρ                SP                            ⁢                              t                SP                                      +                                          ρ                P                *                            ⁡                              (                                                      t                    AP2                                    +                                      t                    AP1                                                  )                                      +                                                                                          ρ                AFS                            ⁢                              t                AFS                                      +                          AR                              F                /                SP                            *                        +                          AR                              P                /                SP                            *                        +                          2              ⁢                              AR                                  P                  /                  AFS                                *                                      +                                                                          AR                              Cap                /                F                                      +                          AR                              P                /                AF                                                        
where xcex2,xcex3, xcfx81, and ARx/y are bulk spin asymmetry, interface spin asymmetry, resistivity and interface resistance, respectively. It can be seen that the Axcex94R is at a minimum value when the two AP sublayers have the same thickness. Such an arrangement is not desirable for a CPP-MR head. Accordingly, an SV structure having a single pinned layer may instead be preferred for CPP-MR head applications. However, as discussed above, a transverse bias supply is still desired in CPP-MR arrangements in order to achieve an optimum linear response.
Accordingly, the present invention is directed to a current perpendicular-to-the-plane magnetoresistance read head having transverse biasing and enhanced magnetoresistance that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a current perpendicular-to-the-plane magnetoresistance (CPP-MR) read head includes a spin valve arrangement and a transverse bias means for providing a transverse bias to the spin valve arrangement.
In another aspect, a magnetoresistance read head having a stacked structure includes a fixed layer having a magnetization direction pinned in a particular direction, a free layer having a magnetization that is free to rotate in varying directions, and an in-stack transverse bias arrangement providing a transverse bias to the free layer.
In another aspect, a method of magnetically biasing a current perpendicular-to-the-plane magnetoresistance (CPP-MR) read head having a stacked structure is provided. This method includes generating a current in a spin valve structure in the CPP-MR read head, and magnetically biasing a free layer of the spin valve structure in a transverse direction with an in-stack transverse bias arrangement.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.